adj. Different from what is usual or common; unusual; singular; peculiar; unique; strange.

from The Century Dictionary and Cyclopedia

Single; sole; singular; especially, single as rendering a pair or series incomplete; lacking a match; being of a pair or series of which the rest is wanting: as, an odd glove; two or three odd volumes of a series.

Singular in excellence; unique; sole; hence, peerless; famous.

Singular in looks or character; peculiar; eccentric; at variance with what is usual: as, an odd way of doing things; an odd appearance.

Leaving, as a number, a remainder of one when divided by two: opposed to even.

Numbered with an odd number: as, the odd files of a company (that is, the files numbered 1, 3, 5, and so on).

Left over after pairs have been reckoned; by extension, remaining after any division into equal numbers or parts: thus, the division of sixteen or nineteen among five leaves an odd one or four odd.

Remaining over after, or differing from, the just or customary number.

Additional to a whole mentioned in round numbers, or to any other specified whole: following and after a number or quantity, or without and when it takes the place of a unit appended to a ten.

Not included with others; not taken into the common account; sporadic; incidental; casual: as, a few odd trifles; to read a book at odd times.

What's odd is that I haven't been reading many long mystery series lately where the author is still alive and writing -- the series I've been reading have been bifurcating into "new and ongoing but short" and "old and finished but long."